Organic materials, whether natural or synthetic, are conventionally protected against degradation by ultraviolet (UV) light by incorporating a UV light stabilizer in the material. Many classes of compounds are known to be useful UV light stabilizers, some being more effective than others. Particularly effective compounds, which provide compositions resistant to degradtion by UV light, include the decahydroquinolines disclosed in copending U.S. patent applications Ser. Nos. 697,345 and 697,387, now issued as U.S. Pat. Nos. 4,073,770 and 4,069,195 respectively; the 1,5-diazacycloalkanes and 2-keto-1,5-diazacycloalkanes disclosed in copending U.S. patent Ser. No. 835,069; and, the 2-keto-1,4-diazacycloalkanes disclosed in co-pending U.S. patent application Ser. No. 835,065. Other cycloalkanes useful as UV light stabilizers are disclosed in Ger. Offen. No. 2,315,042; Japanese Pat. Nos. 7,453,571 and 7,453,572; and in U.S. Pat. Nos. 3,919,234, 3,920,659 and 3,928,330 which teach substituted piperazinediones.
The substituted piperazinediones are difficult to prepare, particularly with dialkyl substituents on each of two N.sup.4 -adjacent symmetrical carbon atoms (hereafter "symmetrical C atoms"). Once prepared, however, they may be reduced to the tetraalkyl substituted piperazine as disclosed in U.S. patent application Ser. No. 239,350 (Ger. Offen. No. 2,315,042). There is no suggestion as to how a mono-keto structure, that is a 2-keto-1,4-diazacycloalkane structure, may be prepared with a total of two or more (hence "polysubstituted") substituents on symmetrical C atoms.
It is known that 4,4,6,6-tetramethyl-1,5-diazacycloheptan-2-one may be prepared by a Schmidt's rearrangement of a six-membered ring with sodium azide (see German Pat. No. 2,428,877) but there is no known manner of similarly arriving at a six membered 1,4-diaza ring with an N.sup.1 -adjacent carbonyl.
It is known 1,4-diaza(3,3,5,5)-dipentamethylene-2-one may be prepared, starting with cyclohexanone by cyclization of bis (1-cyanocyclohexyl) amine, reducing with lithium aluminum hydride to form 1,4-diaza(2,2,5,5)-dipentamethylene-2-imino, treating with acetic anhydride and heating with hydrochloric acid. This procedure is set out in greater detail in an article by Helmut Egg in Monatshefte fur Chemie 106, 1167-1173 (1975). However, starting with acetone instead of cyclohexanone, the reactions do not proceed in an analogous manner to give 3,3,5,5-tetramethyl-piperazin-2-one. This Egg reference teaches substituted piperazines wherein each symmetrical N.sup.4 -adjacent carbon is part of a six membered ring and the cyclic substituent on each N.sup.4 -adjacent carbon is always the same. A single cyclic substituent on the N.sup.4 -adjacent C atom of the fixed two-carbon bridge cannot be prepared by following the techniques of Egg.
Cis-3,3-dimethyl-decahydroquinoxalin-2-one has been prepared from cis-1,2-diaminocyclohexane, and it is disclosed that the cis-compounds are valuable intermediates for the production of pharmaceuticals, textile auxiliary products and synthetic materials. This reference states that the trans-1,2-diaminocyclohexane is converted, with excess chloracetic acid, or with salts thereof, into 1,2-diaminocyclohexane-N,N'-tetraacetic acid, which is quite unlike the behavior of the cis starting material. The cis-2-keto-1,4-diazacycloalkane is prepared by reacting an aqueous solution of cis-1,2-diaminocyclohexane with acetone cyanohydrin, and heating the reaction solution to dryness. The reference does not teach formation of a trans-5,6-polyalkylene-2-keto-diazacycloalkane, and there is no suggestion as to how it could be made. In fact, it is to be understood that the trans-2-keto-1,4-diazacycloalkane cannot be made, since Bindler states that cis-1,2-diaminocyclohexane behaves differently from trans-1,2-diaminocyclohexane; the positioning of the two primary amine moieties imparts distinctly different properties to the isomers. This difference, and particularly the essential difference in cyclization behavior of the primary amine moieties, is used to advantage in the separation of the isomers. The cis isomer cyclizes and complexes with Ni and Cu; the trans isomer does not. Nevertheless we have found that trans-2-keto-1,4-diazacyclohexane can now be formed in a manner analogous to that in which the cis-2-keto-1,4-diazacyclohexane is formed.
Following the teachings of Bindler, ethylene diamine may be substituted for cyclohexanediamine, and 3,3-dimethyl-2-keto-piperazine is obtained. However, when a substituted ethylene diamine is used, the substituents appear on the No. 6 carbon of the diaza ring. For example with 1,2-propane diamine, 3,3,6-trimethyl-2-keto-piperazine is formed; and with 2-methyl-1,2-propane diamine the compound obtained is 3,3,6,6-tetramethyl-2-keto-piperazine. No. 6-substituted and 3-substituted carbons are not symmetrical carbon atoms about the same N-adjacent atom in the diaza ring (hereinafter referred to as "symmetrical N-adjacent C atoms"). These compounds are quite unlike the novel compounds claimed. Moreover, 3,3,6,6-tetraalkyl substituted diazacycloalkan-2-ones, in which the substituents are not on symmetrical N-adjacent C atoms, are relatively ineffective UV stabilizers, confirming my experience that the more substituents on symmetrical N-adjacent C atoms, the better the stabilization effect.
It is known that 2,2,4-trimethyl-tetrahydroquinoline can be hydrogenated to form a mixture of cis and trans 2,2,4-trimethyldecahydroquinoline, and, in general, the trans isomer is the major constituent. However, 2,2-dimethyltetrahydroquinoxaline is not hydrogenated in an analogous manner.
It is to the problem of synthesizing polysubstituted 2-keto-1,4-diazacycloalkanes, efficiently and economically, so that they can be manufactured for commercial use, that this invention is directed.